1. Field of the Invention
The invention is directed to an improved fuel injection apparatus for an internal combustion engines.
2. Description of the Prior Art
A fuel injection apparatus of the type with which this invention is concerned is known from EP 0 987 431 A2. This fuel injection apparatus has a high-pressure fuel pump and a fuel injection valve connected to it for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston, which the engine sets into a stroke motion and which defines a pump working chamber. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve member, which controls at least one injection opening and which the pressure prevailing in the pressure chamber can move in the opening direction, counter to a closing force, in order to open the at least one injection opening. A first electrically actuated control valve is provided, which controls a connection between the pump working chamber and a relief chamber. A second electrically actuated control valve is also provided, which controls a connection between a control pressure chamber and a relief chamber. The pressure prevailing in the control pressure chamber acts on the injection valve member at least indirectly in a closing direction and the control pressure chamber is connected to the pump working chamber. For an injection of fuel, the first control valve is closed and the second control valve is opened so that high pressure cannot build up in the control pressure chamber and the fuel injection valve can open. When the second control valve is open, however, fuel drains out of the pump working chamber by means of the control pressure chamber, so that of the fuel quantity delivered by the pump piston, the fuel quantity available for injection is reduced and so is the pressure available for the injection. As a result, the efficiency of the fuel injection apparatus is less than optimal.
The fuel injection apparatus according to the invention has the advantage over the prior art that for the fuel injection, when the injection valve member is opened with a maximal stroke, the second control valve can be closed so that no loss in fuel quantity and fuel pressure occurs during the injection, thus improving the efficiency of the fuel injection apparatus.
Advantageous embodiments and modifications of the fuel injection apparatus according to the invention are disclosed. In a simple way, one embodiment makes it possible that when the injection valve member is only opened with a partial stroke, due to the small through flow cross section and the resulting throttling action, the sealing surface of the injection valve member has less force exerted on it in the opening direction than when the injection valve member is opened with the maximal stroke, when the throttle action is less intense due to the greater through flow cross section and therefore the pressure and the force acting in the opening direction are greater. Another embodiment permits the control of a preinjection by means of the second control valve, and a further embodiment permits the control of a main injection by means of the second control valve. A further embodiment permits the control of the march of pressure during a main injection by means of the second control valve.